We propose a randomized, controlled trial of a telephone-based, brief insomnia treatment in primary care in order to accomplish the goal of improving psychosocial functioning in post-deployment Iraq and Afghanistan Veterans who meet criteria for Insomnia Disorder. The primary outcome for the trial will be psychosocial functioning, with insomnia severity serving as the secondary outcome. Additional goals include evaluating durability of treatment gains and obtaining feedback from participants about the utility and feasibility of the proposed insomnia treatment. One hundred Iraq and Afghanistan Veterans with Insomnia Disorder will be randomly assigned to either Brief Behavioral Treatment for Insomnia (BBTI; one 60-minute and one 30-minute in-person encounter, and two 20-minute phone-based encounters) or a Progressive Muscle Relaxation Training control group (manualized relaxation training delivered by two in-person and two phone sessions, matched to the BBTI condition for therapist time). Prior to randomization, participants will complete clinician-administered, mental health diagnostic interviews at baseline (and post-treatment). Psychosocial functioning, insomnia severity, and other related self-report measures will be completed at baseline (pre-treatment), mid-treatment, post-treatment, and at 6-month follow-up (active treatment group only). Sleep parameters (e.g., sleep diaries, rest activity) will be completed with a sleep diary mobile application and the Basis wristband (Basis Science Inc., San Francisco) and associated mobile application that tracks sleep cycles and sleep and waking movement, which will be provided for each participant. One week of sleep parameters data will be collected at baseline as well as post-treatment (and at 6-month follow-up for active treatment group only). Both groups will also collect sleep parameters data during the four-week intervention period. We will conduct post-treatment evaluations with the experimental group to help determine the utility of BBTI as well as how the intervention may be improved for Iraq and Afghanistan Veterans. Veterans who received BBTI will complete a feedback questionnaire that will inquire about various aspects of the treatment. The goal is that 75% of Veterans will report that the treatment is feasible and acceptable in various domains, as measured by a rating of three or higher on a five-point Likert scale. Veterans who complete BBTI also will be asked to participate in a 30-minute feedback interview reviewing ratings of each of the domains, as well as most and least helpful aspects of the treatment, data which will be audio recorded and coded. These post- treatment interviews with Veterans will yield suggestions on how the treatment can best be improved for Iraq and Afghanistan Veterans and be implemented in primary care settings. Trained coders will be asked to categorize areas identified by Veterans as helpful and areas noted as needing improvement until no new categories are identified (e.g., thematic saturation). These suggestions will be systematized and used to prepare the treatment for implementation with Iraq and Afghanistan Veterans in primary care. This trial will provide useful information regarding rehabilitative outcomes, and it will yield specific information that will allow us to modify BBTI, ensuring a tailored product based on Veteran feedback.